Luminoth sentry pods appear in Metroid Prime 2: Echoes. They are levitating, spherical units that appear in the Ing Hive's Hive Dynamo Works, where they float up and down continuously. Their exteriors are comprised of the same material as Spider Ball Tracks on Aether, and have red spherical points on them, from which Samus can propel herself. They are used by Samus to access the Key of C-Rch, one of the Sky Temple Keys.
Similar spheres covered with Spider Ball Tracks and red points are seen in the Reactor Core.
"Object scan complete. This is a Luminoth sentry pod. Anti-gravity thrusters online. Magnetic defense field active. Unit is no longer transmitting security data. It appears to be in a holding pattern."